The invention relates to a venting system for an automobile vehicle fuel tank.
The invention relates more particularly to a venting system for an automobile vehicle fuel tank of the type in which a valve is provided with a ball which is placed in a chamber into which open an inlet orifice which has an axis and is connected to the tank and an outlet orifice, one orifice opens onto the center of a concave top face of a bottom wall of the chamber, the ball bears on the concave top face so that, when the vehicle is stopped and is substantially horizontal, the weight of the ball places it at the center of the concave surface where it closes the orifice whereas the ball is moved away from the orifice by vibrations generated by starting or movement of the vehicle and enables venting of the tank.
In the above type of system the top face of the inside wall of the chamber is usually circular and frustoconical with a vertical axis so that as soon as the vehicle is stopped the ball drops to the bottom of the cone to shut off the orifice at the center of the cone.
The angle at the apex of the cone is dictated by a number of parameters related in particular to the maximum inclination of the vehicle when stopped and the size of the ball, its size conditioning its weight and therefore conditioning closing of the valve when filling the tank causes a positive gas pressure in the tank which must not escape via the venting system.
This latter parameter, which conditions the sealing effect of the valve when the vehicle is stopped, therefore makes it necessary to arrive at a compromise between the diameter of the ball and the angle at the apex of the cone formed by the top bearing face of the valve. To avoid using a ball of excessively large diameter it is therefore necessary to use a bearing surface having a relatively small angle at the apex.
Using a small angle at the apex means that the ball remains substantially at the center of the frustoconical surface, even when the vehicle is moving, and thereby interferes with the flow of the gases through the valve.
An object of the invention is therefore to propose a new venting system of the above kind which reduces the size and therefore the cost of the ball and also satisfies simultaneously two contradictory requirements, namely a good seal of the valve when the vehicle is stopped and free flow of the gases through the valve when the vehicle is moving.
To this end, the invention proposes a venting system for an automobile vehicle fuel tank of the type in which a valve is provided with a ball which is placed in a chamber into which open an inlet orifice which has an axis and is connected to the tank and an outlet orifice, one orifice opens onto the center of a concave top face of a bottom wall of the chamber, the ball bears on the concave top face so that, when the vehicle is stopped and is substantially horizontal, the weight of the ball places it at the center of the concave surface where it closes the orifice whereas the ball is moved away from the orifice by vibrations generated by starting or movement of the vehicle and enables venting of the tank, characterized in that the inclination to the horizontal of the concave top surface decreases in the radial direction away from the axis.
According to other features of the invention:
the inclination varies continuously;
the inclination varies discontinuously;
the concave top face includes a frustoconical central first annular part around the orifice to be closed, with its larger end at the top, which has a vertical axis and forms a bearing surface for the ball when the latter is in the closing position, and in that the concave top surface includes a frustoconical peripheral second annular part, around the first part, also with its larger end at the top, which has a vertical axis and whose angle at the apex is greater than that of the bearing surface so that it has a shallow slope;
the peripheral part has an angle at the apex of the order of 160 degrees;
the bearing surface has an angle at the apex of the order of 145 degrees; and
the ball has a diameter of approximately 12.7 mm.